The invention relates to a hybrid method for the coating of a substrate by a thermal application of the coating materials. Thin films with specific material structures and with layer thicknesses in the range from 1-800 μm can be produced with the method.
The substrate is coated in that a coating material is applied using a thermal process jet. The process jet forms a space through which plasma flows and in which the coating material is transported together with a process gas mixture. The plasma is produced by means of an electrical gas discharge, electromagnetic induction or microwaves. An advantageous method in which a particular process jet is produced is described in U.S. Pat. No. 5,853,815. A so-called LPPS thin film (LPPS=low pressure plasma spraying) is applied to the substrate using this method.
A conventional LPPS plasma spraying method is modified in a technical process manner with the LPPS thin film process. The coating material is injected into the plasma in powder form and with a delivery gas. A strong spatial expansion of the plasma results in a “defocusing” of the powder jet. The powder is dispersed to form a cloud and is melted due to a high enthalpy of the plasma and is, optionally, partly evaporated. The coating material arrives at a widely expanded surface of the substrate in a uniform distribution. A thin layer is deposited whose layer thickness is less than 10 μm and which forms a dense cover due to the uniform distribution. A thicker coating with special properties can be produced directly by a multiple application of thin layers.
Such a coating can be used as a functional layer. A functional layer, which as a rule includes different part layers, can be applied to a base body which forms the substrate. For example, for gas turbines (stationary turbines or airplane engines), which are operated at high process temperatures, the vanes are coated with a first single-layer or multi-layer part film such that the substrate becomes resistant to hot gas corrosion. A second coating—of ceramic material—applied to the first part layer forms a heat insulating layer. A method is described in EP-A-1 260 602 for the production of such a heat insulating layer system in which a plurality of individual layers (barrier layer, protective layer, heat insulating layer and/or smoothing layer) can be applied by a changing setting of controllable process parameters in one working cycle. The process parameters are the pressure and enthalpy of the plasma, the composition of the process gas and the composition and the form of application of the coating material.